I found a few threads on this and it looks like a straight forward swap. A few questions you might know the answer to (and it might save me a bunch of time poking through the brake parts catalog at the parts store). The 8.8 might hold up just fine, but I tow 4000-8000 lbs occasionally and the torque plus dragging weight concerns me, plus the later 9.75 is an easy way to get discs and with careful shopping also upgrade to an LSD as well.

-Concerning 97-03 F150s, are all the disc brake rears 9.75 and all the drum rears 8.8, or were there drum 9.75s and disc 8.8s?
-Are the brake systems totally different, or is it just a simple prop valve or MC difference? Mine doesn't have ABS and I won't want to add it either.
-Is it as simple as getting a the 9.75 driveshaft from another Scab shortbed, or did they do something like change tranny output shafts over the years?
-any other finer points you can offer to help make this go smoothly? I'm a hot rodder by trade, but this is my first F150 so the learning curve is a little steep.

Thanks

 

first... you are hauling 8000 pound loads without a 5.4? what motor do you have?

anyway. if you swap from drum to disc you will need a few of the braking components, not sure on what but there was a write up on here about it somewhere.

Are you at stock ride heigth? If so then you MIGHT have to have your driveshaft shortened or get on out of the truck with the 9.75. The drive shafts are extremely variable. Cab size, motor size, bed length, and axle type all play parts in the length of the drive shaft.

The 9.75 is about 2" longer in the front then the 8.8, so if you are lifted any you should be ok.

 

Why does everyone ask me that? Stock tow rating is 7300 with the 4.6 and 8000 with the 5.4. Raw power doesn't make tow capacity, the truck does. Sure, it might stress that little engine, but it tows it just fine. Tow ratings are numbers that the manufacturer suggests to cover their butts under warranty. How much it actually will adequately tow is a whole different thing. I've had two 4.6s in F150s now that have towed the same 8000-lb trailer across the country (L.A. to Rochester) several times with no issues. My last truck (a 99) eventually started giving up the tranny at 176k.

Aside from that, it currently has a 4.6, but I'm in the process of swapping in a 4BT making about 300 hp and 550 tq, so no worries on oomph. The 4BT swap is one of the reasons for the 9.75 swap. I don't want to send 550 lb-ft of torque to an 8.8.

I'm at stock height. I'll scope around and see if I can find the right shaft from a donor truck, if not I'll shorten this one. I'll eventually need a custom shaft anyway for the ZF 5 speed that will go behind the 4BT, but the 9.75 swap will probably happen long before the 4BT/5 speed swap. Thanks for the help.

 

going 4bt... P-pump?

anyways if you are planing on that much power id say ditch the idea of the half ton axle all together. I know there are some crazy lightnings out there cranking some serious power though the 9.75, but they arent towing, and diesel torque is different then the torque curve of a gas motor even a powerfull gas motor.

id do a D60 axle and have custom shafts made to accept the 5x135 bolt pattern. IF you are set on running the 9.75 look into chromoly axle shafts, and some traction bars.

ive seen the 4bt break engine mounts its a torquey engine in stock form. Im eventually putting that or a 6b in my truck. But mine is on D60's and 40" tires.

anyways if you want to try the 9.75 you could easly do it but id deffinitely recommend building the axle to hell and back. and consider adding 4.10 gears to it as well.

another option could be a sterlin 10.25 but that would also need some custom work if you want to run the 5x135 patern.

 

Yes, P-pump, but VE isn't out of the question at the 300-hp level.

I like how you think on overkill. I am in the process of building a 66 Bonneville. Originally I had a Caddy 500 in it, but I think I've settled on a Duramax instead. I have a 10.5" FF GM rear axle in it, and I adapted the front spindles from a 3/4 ton to keep the 8-lugs up front too. At first glance it looks pretty normal, but then you count the lugs

I could do a similar thing with the F150; instead of worrying about adapting a Sterling to 5x135, I could keep the 8-lug out back and adapt the front to 8 lugs as well. Why modify "down" when I can upgrade the front as well?

 

well its the same one way or another you will want matching lug patterns

not sure what you mean by over kill??? but anywho.

Not sure how you would adapt the stock frontend to 8 lug, it would definitely take some work. im sure it can be done though.

Or do like me and rip out everything and slide in 1 tons. But thats a different story. lol and i dont think you want to lift your truck too much. Correct me if im wrong

 

hey Curtis73, you got a build thread for that engine swap? id love to see that thing with the diesel in it.

 

97-98 9.75's contain drum brakes. 99- present 9.75 contains disc brakes. the 9.75 has held up to the abuse of highly modified Lightning F-150's, and in its built form has been comparable to a Dana 60. yes, you'll need to shorten the driveshaft, or find a "new" one in the salvage yard.

or, you could swap the back to a sterling 10.25, and get the hubs off of a 7700 F-150/F-250 LD you would have a seven lug on both axles.

 

10.25 is a 8x170mm bolt pattern

the only way to get it in 7 lug is from the 7700 or custom make the shafts.

and yes a 9.75 built can be as strong as a stock D60 but there is a bigger aftermarket help for the D60.

 

Haven't started the swap yet on either. I had a 4-page build website for the Bonneville, but I took it down for space reasons. The bonneville is completely torn apart. I got as far as the mechanic/chassis stuff done; front suspension has 3/4 ton spindles with 8-lug brakes. I modified the stock lower arm for the truck ball joint, and the upper arms I fabbed up really quick just to get it on the road. The tranny was a TH400 with a gear vendors. rear axle is a 10.5" FF which didn't need to be shortened at all. I just welded on the proper brackets and bushing bosses to convert it to a trailing arm/coil spring rear. I got it all mechanically mostly ready, then I tore it apart. Right now it looks something like this:



The truck I just got. Its exactly what I wanted... except its not diesel. I had $5000 to spend on a truck, and that doesn't buy much of a diesel here in Texas. So the plan could have been to put $5000 down on a diesel and finance the rest, but I'm buying a house so new liabilities aren't good. Instead, I paid cash for a gas truck, and I'll put what I would have been making as payments in the piggy bank for the 4BT swap.

The 4BT is my absolute first choice, but from what I understand its a pain to get it to fit the 4x4. Its pretty easy if you go solid axle and lift it 3", but I don't plan on that.

More as things develop.

 

yeah ive heard that aswell. im geussing clearance issues with the front diff.

Mines gonna be well away from everything so it should slide in nicely.

now i got to make up my mind on 4bt or 6b Im really leaning towards 4bt they are easy to upgrade can make PLENTY of torque and get AMAZING mileage. Plus i believe i can put a stock one infront of my transmission after its built. I might buy a totaly built transmission as well. Says it will hold 600HP which will be plenty. My concern is that it doesnt say how much torque the transmission will take. Its from MONSTER transmission the price is 1700

heres a link
http://racetransmissions.com/store/p...roducts_id/274

and by any chance you know what the 4bt weighs?

 

I was told that depending on accessories and other options, the 4BT weighs in at about 700. The 6BT is more like 1000-1100.

I'm sticking with the 4BT primarily for weight and length reasons, but also because they can be just as torquey and powerful as a warmed-over 6BT, and reports keep coming in of 30+ mpg in 1/2 ton trucks and compacts with the 4.

I think I'll back mine with a ZF 5-speed from a 7.3 truck. I can get an automatic to take the torque, but A) its expensive and B) I want a manual anyway.

 

yeah, thats cool.

i think my 4.2 only weighs in at 300-500 pounds and that is just a geuss. ive had the motor out of the truck and it was heavy but not that bad.

so that geuss might be WAY off.


and yeah that 30+ MPG is looking really really good.

Im wondering on how a 4bt, 1 ton axles, 5.13 gears and 40's would do... i bet it would be a nice little rig.

 

I have the urge to ditch the 3.55s and go with 33s and 4.10s, but for now I'm keeping an eye on streetable MPG. The 33s would look good, but I will never need them. Truth be told, I didn't even want 4x4, but it happened to be in the right truck at the right price so I got it. I'll use the 4x4 about 4 times a year; Twice a year to launch and retrieve my boat on a dirt launch ramp, and twice a year having fun on my friend's ranch.

As far as converting the front to 8-lug it might be simpler than you think. At least on 2wd its really simple. I've done it before by mixing and matching steering knuckles and ball joints, and once I pressed the actual spindle out of the knuckle, machined the hole in the knuckle, and pressed in the right shaft for the larger bearings. That was a GM, so caliper interchanging was easy... but I imagine a 4x4 will be a whole different animal. I'll have to take it apart and look at it, see what I can dream up.

My main goal is to upgrade the rear axle, then use a 4BT/ZF combo. I'll have to look at the options as to whether or not its easier/cheaper to keep the 5-lugs on the back, or to upgrade the front to whatever the back ends up being. I like the Sterling axle. Its a lot like the GM 10.5, but you don't have to pull the axles to do the brakes

I don't know how much the 4.2 weighs; probably 400 or so. I know an assembled 302 is about 525lbs, more like 575 fully dressed with accessories and iron manifolds. A 4.6 is about 475-500, but that is not actual weight just internet guesses.

 

Trimble, I was referring to the 7700 version of the sterling 10.25. by swapping in the 7700 version of the 10.25, and the 7700 hubs, he could convert to a seven lug system w/ matching bolt patterns.

swapping in a solid axle will require at least six inches of lift due to the presence of the huge IFS frame crossmember, unless you cut the SOB out and reinforce the frame with a straight crossmember that doesn't hang down so far. you don't want the frame smacking the front differential, right?